The PlaneMon DMT monitor (author: Evan Goetz) tracked acoustic noise in 5 widely separated microphones at LHO and in 3 microphones at LLO during the S5 run and reported in real-time on suspected aircraft overflights. Triggers were based on elevated acoustic noise in more than one microphone and/or on fitting to the characteristic Doppler shifted trajectory of a plane passing nearby. Most detections were of airplanes, but helicopters occasionally triggered the monitor too.

The monitor created an archive of triggered events, broken up by months, for both LHO and LLO.

I have hand-scanned a sampling of these 45,000 triggers (many aircraft produced multiple triggers with overlapping 2-minute intervals) to assess what criteria should be used to insert data quality flags in the database. I concluded that nearly all triggers in the archives warrant flagging as "likely" aircraft and that most of them should be considered "very likely".

My somewhat subjective criteria for flagging a trigger as "very likely" are elevated noise in three (or more) microphones and/or at least one successful Doppler trajectory fit.

Here is one example of a trigger where only one microphone channel has a successful fit.

Here is one example (atypical) of a trigger where all five microphone channels at LHO have a successful fit.

Here is a more typical example of a 5-fit trigger where not all of the "successful" fits are sensible.

Here is one example of a trigger where multiple microphones trigger, but for which there is no successful trajectory fit because the trajectory simply doesn't follow the nominal "lazy S" model.

Applying these criteria give the following DQ flagged intervals:

AIRCRAFT_LIKELY	AIRCRAFT_VERY_LIKELY
LHO (32691)	LHO (29697)
LLO (12561)	LLO (10641)

Here are the raw PlaneMon outputs for LHO and LLO from which these flags are derived. Here are summary tables for LHO and LLO giving the numbers of microphone channels with high activity and the number of fitted trajectories.

Note: Aircraft do not necessarily create trouble for the interferometers, despite our unfortunate experience in the S2 run. Acoustic couplings were greatly mitigated before the S5 run. These aircraft flags should probably be used only for guidance in candidate follow-ups, where measured couplings are used to estimate influence on DARM_ERR, not as a priori vetoes.

K. Riles - May 30, 2008